Carburetor

ABSTRACT

This invention relates to a fuel circulation type and floatless carburetor having an overflow chamber and fuel supply and discharge pumps located on opposite sides of the carburetor suction passage. In order to provide an inclination insensitiveness, the carburetor fitted with a fuel-level forming and exposed fuel surface-maintaining chamber and a fuel return chamber cooperatably arranged with each other, is characterized by the provision of a suction side fuel pump leading hydraulically from a fuel supply source to the first chamber and a discharge side fuel pump leading from the second chamber back to said supply source, said pumps being of pulsative diaphragm type and positioned in close proximity to said bore and in a substantially opposed arrangement relative to each other and about said bore, said second pump having a substantially larger capacity than the first pump for the prevention of fuel leakage through an air vent passage.

Muted States Patent 1191 1111 3,834,070 Miyazalti Sept, 10, 19M

[54] CARBURETOR 3,472,211 10/1969 Meininger 26l/DIG. 68 [75] Inventor: Toyoshige Miyazaki, Tokyo, Japan FOREIGN PATENTS OR APPLICATIONS 73 Assignee; K ihi S iki Manufacturing C 12,223 1921 Great Britain 261/72 R LtdL, Kanagawa-ken, Japan P E T R M] rzmary xammer- 1m res [22] Flled: 1971 Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, [21] Appl. No.: 174,101 Zmn & Macpeak [30] Foreign Application Priority Data 7 [57] ABSTRACT Aug. 21, 1970 Japan 45-73275 This invention relates to a fuel circulation type and floatless carburetor having an overflow chamber and 52 us. 01.. 261/36 A, 261/DIG. 50, 261/DIG. 68, e Supply and dlscharge p located 911 91 2 1 A sides of the carburetor suction passage. [51] lint. Cl. F02m 17/04 In order to provide an inclination insensitiveness, the [58] Fieid 01? Search 261/35, 37, 69 A, DIG. 68, carburetor fitted with a fuel-level forming and exposed 261/36 A; 123/139 AH, 139 A, 139 AB, 139 fuel surface-maintaining chamber and a fuel return BA, 139 AN, 139 AV, DIG. l2, DIG. 5; chamber cooperatably arranged with each other, is 417/380, 381, 382, 395, 521, 522 characterized by the provision of a suction side fuel pump leading hydraulically from :a fuel supply source [56] References Cited to the first chamber and a discharge side fuel pump UNITED STATES PATENTS leading from the second chamber back to said supply I 567 807 12/1925 Mock 261/72 A source, said pumps being of pulsative diaphragm type 1 727 197 9/1929 Br an 5Z1: IIIIIIIIII 2E1/D10. 37 and Positioned in Close Proximity to Said bore and in a 1:797:165 3/1931 Tice 261/69AX Substantially ppo ed rrangement relative to each 1,849,720 3/1932 other and about said bore, said second pump having :1 2,031,379 2/1936 substantially larger capacity than the first pump for 3,085,620 4/1963 the prevention of fuel leakage through an air vent 3,161,700 12/1964 passage. 3,181,843 5/1965 3,236,217 2/1966 Phillips 261/DIG. 68 6 Claims, 8 Drawing Figures 28 2] J T 0 h 103 11 21 32 1 2 T, W 24 i Q .Q. 20 1 18' 1a 19 25" 24 I I] E\==, -E7ZL 18 9 iii 24 u 22 9 /25 22 1 100 Li -1 3i L PAIENIEDsEP 1 man SHEEI 1 BF 4 PIIIEIIIEIISEPIO III 3.034.676

sum 3 0F 4 P F I 0. 5 A 60 D|SCHARGE t PUMP CAPACITY 50 b'o A O @400 4 o b 5 '///\3SUCT|ON PUMP g x/ CAPACITY 5 2O I O I Q ENGINE FUEL 2 coNsuMPTIoN I) 0 A Q.

9 l I I500 2000 8000- RPM IDLING FULL THROTTLED ENGINE REVOLUTIONS PER MINUTE CARBURETOR This invention relates to improvements in and relating to carburetors. More specifically, it concerns with fuel circulation type carburetors.

The fuel circulation type carburetors are known in various different designs structures. A common feature of this type of carburetor resides in such that the fuel fed from a supply source is passed through an overflow means such as dam, slit, opening or the like provided in a fuel level maintaining chamber of the carburetor and the overflowed fuel is returned back to the supply source. In this way, a constant fuel level is always and automatically maintained within the chamber, and indeed, without use of a control mechanism for maintaining the desired constant fuel level, such as that comprising a control float, a valve controlled thereby and a seat for cooperation with the valve. In this way, such a frequently encountered conventional drawback that foreign particles conveyed by the supplied fuel such as dusts, machined chips are deposited on the valving surfaces, resulting in a defective operation of the floatcontrolled valve means, an unintentional rise of the fuel surface and fuel bleed into the suction passage of the carburetor, can effectively be avoided. A further advantage of the improved type of carburetor resides in such that thanks to lesser number of frictional machine components, a reliable and durable cost and fuel level control performance can be assured over a longer service life, even fitted on a severe drive engine subjected to substantial degree of vibration during its operational period.

On the contrary, however, a substantial drawback inherent in the above improved type carburetor is such that the predetermined fuel levels to be relatively main tained in the fuel return chamber fuel discharge passage of the carburetor and in the fuel supply source are subjected to appreciable relative changes when the vehicle or other carrying a drive engine fitted with the carburetor is operated at an inclined state. In this case, the return flow of fuel back to the supply source will be substantially reduced from the scheduled rate, resulting in a corresponding rise of fuel level in the fuel levelforming chamber, accompanying an appreciable fluctuation of the fuel level and disturbing a favorable operation of the drive engine. Under extreme conditions, the engine operation will be brought into dead stop. When the throttle valve is suddenly closed from a high speed running condition of the engine under these unfavorable operating conditions, an excess amount of fuel may frequently be accumulated provisionally in the fuel return chamber of the carburetor, which disturbs the engine drive to a considerable degree.

Therefore, the main object of the invention is to provide a fuel circulation type carburetor substantially obviating the aforementioned various conventional drawbacks.

These and further objects, features and-advantages of the invention will become more apparent when read the following detailed description of the invention by reference to the accompanying drawings.

In the drawings: 7

FIG. 1 is a perspective view of a fuel circulation type carburetor embodying the principles of the present invention.

FIG. 2 is a front view of the carburetor shown in FIG. ll.

FIG. 3 is a cross-sectional view thereof taken on the line ll lllllll of FIG. 4, being drawn on somewhat enlarged scale relative to FIG. 2.

FIG. d is a longitudinal section thereof.

FIG. 5 is a chart showing several characteristic performances of the carburetor plotted against engine revolutions per minute.

FIG. 6 is a similar view to FIG. 2, illustrating, how ever, a second embodiment of the invention.

FIGS. 7 and g are respective similar views to FIGS. 3 and 4, yet showing the second embodiment.

Referring now to FIGS. 1 4, the first embodiment of the invention will be described hereinunder in detail.

In these figures, numeral ll denotes a main body of the carburetor, having a horizontal suction passage 2 formed therethrough. A conventional throttle valve 3 is fixedly attached to a horizontally extending lateral pivot shaft 3a which is pivotably mounted at its both ends in the peripheral wall defining the corresponding part of the suction passage, althro'ugh the bearing and mounting means therefor have been omitted from the drawings on account of its very popularity.

A choke valve 4 is attached to a lateral pivot shaft 4a pivotably mounted in the similar way. Numeral 5 represents a small or auxiliary venturi section provided at an intermediate point between the both end openings of the passage 2 and in a projecting way from the bottom thereof. The venturi passage per se is shown at 5a.

A low speed service fuel conduit pipe 6 passes vertically through the auxiliary venturi section 5 and its related part of suction passage 2 and extends by its lower part deeply into the bottom wall ofthe suction passage. A main fuel conduit piece 7 formed substantially into a sleeve encloses concentrically the lower part of said conduit pipe 6; a concentric fuel passage gap 7a being provided between the both.

Offset from the lower end part of conduit pipe 6, there is provided a fuel return chamber 110 formed in the material of main body l and provided in turn with a stationary overflow dam 9 so as to define a fuel levelfonning chamber 8. The open bottom of fuel return chamber Ml is sealed and closed by a bottom piece through a rubber or the like sealing sheet llltla. The bottom piece 100 is attached fixedly to the main body ll from below, although the fixing bolts have omitted from the drawing only for simplicity.

An air vent pipe ll extends across the suction passage 2 and the both ends of said pipe lll are firmly held in the material of main body I; the upper end of said vent pipe is opened to ambient atmosphere, while its lower end is kept in communication with fuel return chamber 110, and thus fuel level-forming chamber 8.

A main fuel conduit 12 coming from the bottom of chamber 8 (FIG. 3), and being shown only schematically, is led to a fuel passage 1101 (FIG. 4) formed in the bottom piece 100, the intersection between the both is arranged to be regulated by a main fuel regulator valve 13 formed into a manually regulatable needle valve as shown. The upper end of fuel passage I01 opens from below into the friction chamber into which the pipe 6 and the sleeve 7 extend.

The top end of conduit pipe 6 is tightly closed by a screw plug 102, a connecting piping 14, only schematically shown, extends from the outlet 6a of said pipe 6 to a low speed service nozzle 15 opening towards the suction passage 2. A regulating needle valve 16 is provided at an intermediate point of the connecting piping M.

A pulsative diaphragm type fuel suction pump unit, generally shown at 17, is bolted at 103 to the main body 1 ata place close to the suction passage 2, said pump unit comprising a pump drive chamber 18 containing a pulsative diaphragm 20 fixedly mounted at its peripheral zone as shown; a pumping chamber 19 kept in direct communication with the outer half of said chamber 13 defined by the said diaphragm; a check valve diaphragm 21 including suction side check valve part 22 and delivery side check valve 24; respective valve seat pieces 23 and 25; a fuel filter 26 and a suction pipe joint 27 which leads to the fuel supply source, not shown.

An equally pulsative diaphragm type fuel delivery pump unit 28 is attached to the main body 1 in an opposing manner to the unit 17 and by fixing bolt means similar to those as at 103, although being omitted from the drawing only for simplicity. The unit 28 consists of a pair of opposing type component pump units, each comprising a pump drive chamber 18' or 18 including respective pumping diaphragm 20 or 20"; a pumping chamber 19 or 19"; a check valve diaphragm 21 or 21 including suction check valve part 22 or 22" and delivery check valve part 24 or 24"; and respective valve seat pieces 23 'or 23" and 25 or 25". It should be noted that the delivery pump unit 28 has a larger pump delivery capacity than the suction pump unit 17.

Numeral 29 represents a fuel inlet passage extending from the outlet side of fuel delivery valve seat piece 25 to the chamber 8. A further passage 30 extends from the chamber to the valve seat pieces 23 and 23". A fuel return space 104 is provided so as to establish a fluid communication with valve seat pieces 25 and 25 when the valve diaphragms 21 and 21" operate, a return conduit 31 extending from the space 104 to the inlet side of the fuel supply source, not shown.

There is provided a conduit network 32, only schematically shown, extends from an engine suction manifold or directly from the engine crankcase, not shown, to pump drive chambers 18, 18' and 18" for driving the respective pumping diaphragms 20, and 20".

The operation of first embodiment of the carburetor according to this invention so far shown and described is as follows. When the engine is brought into operation, pulsative pressure pulses will be transmitted from the engine crankcase through conduit network 32 to pump drive chamber 18, thereby the related pumping diaphragm 20 cooperating with suction side and delivery side valve seat pieces 23 and being brought into pulsative movement and thus 'the effective volume of pumping chamber 19 being increased and decreased intermittently and alternatingly, so as to perform a pulsative pumping action. In this way, fuel is sucked from the supply source, not shown, through suction joint 27, filter 26 and valve seat piece 22 into pumping chamber 119 and thence delivered through delivery side check valve part 24 and fuel inlet passage into the chamber 8.

The thus delivered fuel will flow over the upper end of dam 9 upon establishment of a predetermined fuel level within the chamber 8. This fuel level is constantly maintained.

of its pumping diaphragms 20' and 20" performing pulsative pumping action, respectively.

In advance of the entrance of fuel into the chamber 10, discharge pump unit 28 will suck the air prevailing therein and discharge it. However, when the overflowed fuel enters into the chamber 10, the pump unit 28 will suck it therefrom and deliver it through suction side check valve parts 22' and 22", pumping chambers 19' and 19", discharge side check valve parts 24 and 24 and discharge connection joint 31 back to the fuel supply source, not shown, thus performing the fuel return service.

Fuel supply from the chamber 10 through main conduit pipe 7 and through several members 6, 14, 16 and 15 to the suction passage 2 for preparing air-fuel mixture in a dual way is brought about as is conventional.

As will be seen from the foregoing that during operation of the drive engine, the overflowed fuel from the chamber 8 over overflow dam 9 into the fuel return chamber 10 is being sucked always positively by the discharge pump unit 28 having a larger delivery capacity than suction pump unit 17 and returned through discharge joint connection 31 back to the fuel supply source, not shown. There remains therefore no excess amount of fuel in the chamber 10 to such a disadvantageous degree that the fuel level kept within the chamber 8 will be affected adversely. Since air vent pipe 11 is positioned at the center of suction passage 2 when seen in FIG. 3, a liquid lock of air vent passage 11 by the fuel prevailing in the chambers 8 and 10 which might be disadvantageously invited when the engine operates at a substantially inclined position can be effectively prevented.

In this way, substantially no fluctuation in the pressure at the free fuel level may be encountered irrespective of occasional inclination degree of the engine fitted with the carburetor. Thus, a higly superior inclinationinsensitive carburetor can be provided.

Next, referring to FIG. 5, it is now assumed that the throttle valve 3 is suddenly closed by manipulation of the attached manipulating lever (FIG. I) from the throttle-full opened, engine high speed running position, the engine will continue to run at the high speed for the time being and by virtue of the running inertia owned by the moving parts of the engine and the suction side pump unit 17 will operate to such a substantially large volume of fuel as shown by way of example at b. On the other hand, the fuel demand by the engine must be at a substantially lower rate, as shown by way of example at a in the chart, since the throttle valve has been already closed. 1

Therefore, a substantial amount of excess fuel corresponding to (b a) will overflow from the chamber 8 to 10. However, the capacity of discharge side pump unit 28 has a substantially larger than that of suction side pump unit 17, the excess overflowed fuel into the chamber 10 can be returned rapidly back to the fuel supply source through discharge connection joint 31. Therefore, the fuel level kept in the chamber 8 is not affected adversely, thus assuring optimum running condition over a wide operational range of the engine.

As the both pump units 17 and 28, especially the pump drive chambers 18 and 18, 18" thereof are provided in close proximity to suction passage 2 and in an oppositely arranged way relative to the latter, the heat contained in the pulsating air delivered from the engine crankcase through piping network 32 to said pump drive chambers is effectively utilized to compensate the cooling effect acting upon the main body 1 by the evaporation of the fuel in the passage 2. Therefore, the disadvantageous icing phenomenon can effectively be prevented. 0n the contrary, a temperature rise in the pumping chambers 19, I9 and 19" can be effectively prevented by the transmission thereto of the cooling effect provided by fuel evaporation in the passage 2, thus the disadvantageous and frequentlyencountered vapor lock being substantially obviated.

lFinally, referring to FIGS. 6 8, the second embodiment will be described hereinafter.

In this embodiment, a modified fuel level-forming or establishing chamber 90 of liquid rotary type is provided in the main body 51, as being partially defined by a stationary and upright overflow dam 59. The opening end of fuel inlet duct 91 into the chamber 90 inclines at an angle from above to below and is arranged, although not specifically shown, to open substantially in the tangential direction when seen from above the chamber 90, thereby the liquid fuel contained therein being caused to perform a concentrically rotational flow and thus representing a concavely curved liquid surface specifically shown at 90a. A plurality of air vent passages 92 extend from the liquid level-establishing chamber 90 and a fuel return chamber 60 which is similar to that shown at 10 in the foregoing, and open to the ambient atmosphere, after passage through the material of the main body 51. As seen, each of these air vent passages 92 is provided with a check valve 93, preferably of ball type as shown. Further detail parts of the present embodiment are substantially similar to those employed in the foregoing, irrespective of occasional minor changes in their configuration and arranged position. Therefore, these similar parts are shown by respective same reference numerals, yet each being added with 50 for easy and quick identification and comparison. As seen, the regulator 63 is arranged vertically instead of horizontally in the foregoing. In addition, main fuel conduit piece 57 is formed at its bottom end with a valve seat 57a for cooperation with a pointed relator valve 63.

The operation of the second embodiment is as follows.

When the engine starts to run, pulsative air pressure pulses are transmitted from the engine crankcase through conduit network 82 to respective pump drive chambers 68, 68' and 68", thus the respective pumping diaphragms 70, 70 and 70 being brought into oscillation. By the oscillation of diaphragm 70, fuel is sucked from the supply source, not shown, through suction joint connection 77 to fuel filter 76, thence through inlet duct 91 into the chamber 90 as referred to above to provide a concave liquid fuel surface 90a.

Gradually increased liquid fuel supplied to the chamber 90 and brought into rotation therein will finally overflow through thetop edge of overflow dam 59 and is accumulated in the fuel return chamber 60 as before.

The thus accumulated fuel is taken out from the chamber 60 by the action of the dual type pump unit 78 through the discharge connection joint 81 back to the fuel supply source asbefore.

By the establishment and maintenance of the centrally concave dynamically produced liquid fuel surface 90a within the chamber 90, the inclination insensitive performance of the carburetor according to the present invention is still further accentuated. In this case, the adjustment of the liquid level may be realized by provision of orifice means or similar flow reducing means in the passage 91. Alteration of the position of the latter will serve for the same purpose, although not shown.

In case of an inclination of the drive engine, and thus the carburetor, one or more of check valves 93 may be automatically closed for preventing otherwise possible fuel leakage, while the remaining air vent passage or passages 92 is/are open to vent. In this way, the possibility of fuel leak through air vent passages 92 can substantially be avoided.

Although in the foregoing description, there are provided a plurality of suction side check valves 22' and 22" or 72' and 72" for the discharge side pump unit 23 or 78, respectively. If these valves for the pump unit are properly dimensioned to have the necessary pump capacity, they may be, if required, replaced by a single one. This feature will be naturally applied to the discharge side check valves 24'; 24" or 74-; 741".

The embodiments of the invention in which an exclu sive property or privilege is claimed are as follows:

i. A fuel circulation type carburetor comprising a main body having a suction passage therethrough, a first chamber in said body for receiving fuel from a supply source, a second fuel return chamber formed in said main body of said carburetor, means separating said first and second chambers to allow excess fuel in said first chamber to overflow into said second chamber to maintain a predetermined level of exposed fuel in said first chamber, a fuel suction pump of the pulsated diaphragm type for supplying fuel to said first chamber and a fuel discharge pump of the pulsated diaphragm type for returning fuel in said second chamber to said supply source, each of said pumps being attached to said main body on opposite sides of said suction passage with said discharge pump having a capacity substantially larger than that of said suction pump.

2. A fuel circulation type carburetor as set forth in claim ll wherein each of said pumps is provided with a drive side, said drive sides of said pumps being posi' tiond in close proximity to said suction passage formed through said body with each of said pumps being adapted to be driven by pulsating air pressures supplied from the crankcase of a drive engine fitted with said carburetor.

3. A carburetor as set forth in claim 2 further comprising inlet passage means for conveying pulsating air pressure pulses from the crankcase of a drive engine to the drive side of said pumps, said inlet passage means being provided within the main body whereby the cooling effect provided by the evaporation of liquid fuel is compensated by the heat contained in the air passage from the crankcase.

i. A carburetor as set forth in claim ll, further comprising an air vent passage extending diametrically across said suction passage with one end of said air vent passage being vented to the atmosphere and the opposite end thereof being connected to said first and second chambers.

5. A carburetor as set forth in claim ll, further comprising a plurality of air vent passages extending through said main body with one end of each of said passages being vented to the atmosphere and the opposite end of each of said passages being connected to said first and second chambers and. check valve means disposed within each of said passages to prevent the uration and a fuel inlet passage is provided in said main flow of fuel from said chambers to the atmosphere. body at an angle to said first chamber to provide for the 6. A carburetor as set forth in claim 1, wherein said rotation of liquid fuel within said chamber.

first chamber is provided with a predetermined config- 

1. A fuel circulation type carburetor comprising a main body having a suction passage therethrough, a first chamber in said body for receiving fuel from a supply source, a second fuel return chamber formed in said main body of said carburetor, means separating said first and second chambers to allow excess fuel in said first chamber to overflow into said second chamber to maintain a predetermined level of exposed fuel in said first chamber, a fuel suction pump of the pulsated diaphragm type for supplying fuel to said first chamber and a fuel discharge pump of the pulsated diaphragm type for returning fuel in said second chamber to said supply source, each of said pumps being attached to said main body on opposite sides of said suction passage with said discharge pump having a capacity substantially larger than that of said suction pump.
 2. A fuel circulation type carburetor as set forth in claim 1 wherein each of said pumps is provided with a drive side, said drive sides of said pumps being positiond in close proximity to said suction passage formed through said body with each of said pumps being adapted to be driven by pulsating air pressures supplied from the crankcase of a drive engine fitted with said carburetor.
 3. A carburetor as set forth in claim 2 further comprising inlet passage means for conveying pulsating air pressure pulses from the crankcase of a drive engine to the drive side of said pumps, said inlet passage means being provided within the main body whereby the cooling effect provided by the evaporation of liquid fuel is compensated by the heat contained in the air passage from the crankcase.
 4. A carburetor as set forth in claim 1, further comprising an air vent passage extending diametrically across said suction passage with one end of said air vent passage being vented to the atmosphere and the opposite end thereof being connected to said first and second chambers.
 5. A carburetor as set forth in claim 1, further comprising a plurality of air vent passages extending through said main body with one end of each of said passages being vented to the atmosphere and the opposite end of each of said passages being connected to said first and second chambers and check valve means disposed within each of said passages to prevent the flow of fuel from said chambers to the atmosphere.
 6. A carburetor as set forth in claim 1, wherein said first chamber is provided with a predetermined configuration and a fuel inlet passage is provided in said main body at an angle to said first chamber to provide for the rotation of liquid fuel within said chamber. 